Boring and drilling operations produce chips of removed material adjacent the tool cutting edges, and these chips must be removed if continuous and accurate cutting is to be achieved. A number of "chip breakers" have been utilized with the cutting edges of metal removing tools such as drills, reamers, boring tools, turning tools and milling cutters, and such chip breakers usually employ surfaces or abutments defined adjacent the cutting edge for engaging the chip and abruptly changing its direction, or interfering with its movement, to impose a force on the chip causing the chip to break into small pieces which may be cleared from the cutting location.
During twist drilling operations, the chip is removed at the forward end of the drill where the cutting edge engages the workpiece, and the chip is received within a drill flute. If the hole being drilled is relatively shallow, the chip will usually move through the flute, and is thrown from the drill due to the centrifugal forces existing because of the drill rotation. If the hole being drilled is relatively deep, the chips within the drill flutes cannot be thrown clear, and it is common for the chips to accumulate within the flute and bind against the wall of the drilled hole. In such instance the cutting action of the drill ceases, the drill overheats and may break within the hole. When drilling deep holes the drill must be repeatedly removed from the hole and the flutes cleared before drilling resumes, and a single continuous forward drill movement cannot be maintained. The aforementioned problems also exist in core boring operations where an existing hole is enlarged, and chip accumulation will prevent continuous drilling unless the chips are removed.
When drilling or boring relatively deep holes, or enlarging existing deep core holes, even with the use of lubricating and coolant fluids, the accumulation of chips within the flutes is particularly troublesome, and the chip accumulation prevents the fluid from engaging the tool cutting edge and overheating and accelerated wear of the cutting edge is experienced.
It is an object of the invention to provide a core boring tool capable of quickly enlarging an existing deep hole with a continuous unidirectional axial movement wherein chips of removed metal are quickly removed from the cutting region.
A further object of the invention is to provide an elongated self-cleaning core boring tool for enlarging previously existing deep holes wherein chips removed by the tool's cutting edges are quickly removed from the location of cutting in the direction of tool axial movement.
Another object of the invention is to provide a self-cleaning boring tool of economical construction which is capable of accurately enlarging an existing hole in a minimum of time and with high accuracy.
An additional object of the invention is to provide a self-cleaning core boring tool of elongated configuration capable of enlarging an existing deep hole wherein the tool is piloted with respect to the hole being formed and a high degree of accuracy and tool alignment may be maintained.
Yet another object of the invention is to provide a self-cleaning core boring tool using spiralled flutes to receive chips from the cutting edges wherein the cutting edges are so oriented as to deflect chips into the flutes, and wherein the flutes are spiralled in a direction opposite to that of the tool rotation.
In the practice of the invention the core boring tool is of an elongated configuration having a cylindrical shank defined at the rear of the tool for being received within a chuck or similar rotating tool holder of conventional construction. The central region of the tool comprises a cutting portion and a pair of cutting elements are defined upon the central portion in diametrically opposed relationship. The forward portion of the tool constitutes a cylindrical extension having a pair of spiralled flutes defined therein, and the flutes extend into the central portion adjacent and behind the cutting elements wherein each flute is in communication with a cutting element.
The flutes formed in the forward extension are spiralled in a direction opposite to that the tool is rotated during boring, and chips removed during the boring are deflected toward and into the associated flute for displacement forwardly from the location of cutting to keep the cutting area chip-free.
Preferably, liquid coolant is injected into the hole being formed in the workpiece rearwardly of the cutting elements, and the coolant tends to wash the chips forwardly through the extension flutes. Additionally, a forward pilot is preferably located adjacent the workpiece for receiving the extension during boring and a rear pilot engages the shank whereby the pilots will insure that the tool does not run off-center during cutting.
The cutting elements comprise cylinders of hard alloy, preferably carbide, attached to the tool central portion by screws, and by using cutting tools having a circular periphery the cutting edge makes substantial contact with the workpiece establishing an effective heat transfer between the cutting element and workpiece whereby the cold metal of the workpiece cools the cutting element while the flutes convey away the hot chips. Because of this action a coolant is not always required and the removal of heat by the chips is aided by the fact that the cutting elements are obliquely oriented to the axis of the tool for directing the chips into the associated flute.